Cross Reference to Related Applications
The invention disclosed herein relates to molded case circuit breakers. The following patent applications all relate to molded case circuit breakers and were filed on Aug. 1, 1988: Ser. No. 226,503, entitled CROSS-BAR ASSEMBLY, by Jere L. McKee, Lance Gula and Glenn R. Thomas; and Ser. No. 226,655, entitled COMBINATION BARRIER AND AUXILIARY CT BOARD, by Gregg Nissly, Allen B. Shimp and Lance Gula.
The following commonly assigned U.S. Pat. applications were filed on Oct. 12, 1988 and all relate to molded case circuit breakers: Ser. No. 256,881 entitled SCREW ADJUSTABLE CLINCH JOINT WITH BOSSES, by James N. Altenhof, Ronald W. Crookston, Walter V. Bratkowski, and J. Warren Barkell; Ser. No. 256,879 entitled TAPERED STATIONARY CONTACT LINE COPPER, by Ronald W. Crookston; and Alfred E. Maier; and Ser. No. 256,878, entitled TWO-PIECE CRADLE LATCH FOR CIRCUIT BREAKER, by Alfred E. Maier and William G. Eberts.
The following commonly assigned U.S. Pat. applications also relate to molded case circuit breakers: Ser. No. 260,848, filed on Oct. 21, 1988, entitled UNRIVETED UPPER LINK SECUREMENT, by Joseph Changle and Lance Gula. Ser. No. 07/331,769, filed on Apr. 3, 1989, entitled ARC RUNNER CONTAINMENT SUPPORT ASSEMBLY, by Charles Paton, Kurt Grunert and Glen Sisson; and Ser. No. 07/331,920, filed on Mar. 31, 1989, entitled EXTENDER SPRING FOR INCREASED MAGNETIC TRIP SETTINGS, by Kurt Grunert.
The following two commonly owned patent applications were filed on Apr. 25,1989: Ser. No. 07/343,047, entitled TWO-PIECE CRADLE LATCH, KEY BLOCKS AND SLOT MOTOR FOR CIRCUIT BREAKER, by Alfred E. Maier, William G. Eberts and Richard E. White and Ser. No. 07/342,820, entitled TWO-PIECE CRADLE LATCH, HANDLE BARRIER LOCKING INSERT AND COVER INTERLOCK FOR CIRCUIT BREAKER by A. D. Carothers, D. A. Parks, R. E. White and W. G. Eberts.
Commonly owned patent application Ser. No. 07/374,370 was filed on Jun. 30, 1989, entitled REVERSE SWITCHING MEANS FOR MOTOR OPERATOR, by Kurt Grunert and Charles Paton.
Commonly owned patent application Ser. No. 07/389,849 was filed on Aug. 14, 1989, entitled TRIP INTERLOCK DESIGN, by Kurt Grunert, Ronald Cheski, Robert Tedesco, Michael J. Whipple, Melvin A. Carrodus and James G. Maloney.
Commonly owned U.S. Pat. application Ser. No. 491,329 was filed on Mar. 9, 1990, entitled "PINNED SHUNT END EXPANSION JOINT", by Lance Gula and Roger W. Helms.
Lastly, commonly owned application Ser. No. 503,812, was filed on Apr. 31, 1990, entitled "CIRCUIT BREAKER POSITIVE OFF LINK", by David A. Parks, Yu Wei Chou and Thomas A. Whitaker.
1. Field of the Invention
This invention relates to molded case circuit breakers and more particularly to a multiphase molded case circuit breaker having a phase sensitivity assembly which either trips or reduces the tripping time of the circuit breaker any time an open circuit condition occurs in less than all of the phases in a multiphase electrical device connected to the circuit breaker.
2. Description of the Prior Art
Molded case circuit breakers are generally old and well-known in the art. Examples of such circuit breakers are disclosed in U.S. Pat. Nos. 4,489,295; 4,638,277; 4,656,444 and 4,679,018. Such circuit breakers are generally used to protect electrical circuitry from damage due to an overcurrent condition, such as an overload and a relatively high level short circuit condition. An overload condition is normally 200 to 300 percent of the nominal current rating of the circuit breaker. A high level short circuit condition can be 1000 percent or more of the nominal current rating of the circuit breaker.
Molded case circuit breakers generally include at least one pair of separable main contacts which may be operated manually by way of an operating handle, extending outwardly from the circuit breaker case, or automatically in response to an overload or a high level short circuit condition. In the manual mode and one automatic mode of operation, the separable main contacts are opened by an operating mechanism which, in turn, is actuated by either a trip unit in the automatic mode or the operating handle in the manual mode. In another automatic mode of operation, magnetic repulsion forces, generated between the stationary and movable main contacts during relatively high level overcurrent conditions can also cause the main contacts to be separated independently of the operating mechanism.
In the first mentioned automatic mode of operation, thermal magnetic trip units are used to sense an overcurrent condition. These thermal magnetic trip units are interlocked with the circuit breaker operating mechanism to cause the separable main contacts to be tripped during an overcurrent condition. More specifically, the thermal magnetic trip units are comprised of a thermal unit and a magnetic unit. The thermal unit consists of one or more bimetals which cause the circuit breaker to be tripped during an overload condition. The bimetals are generally disposed in series with a line conductor and thus are subjected to line current. During normal operating conditions, the bimetals are deflected by the line current flowing therethrough but not enough to cause a trip of the circuit breaker. During an overload condition, the bimetals are subjected to additional heat resulting from the increased current flow therethrough which causes additional deflection of the bimetals resulting in tripping of the circuit breaker.
The magnetic unit includes a magnetic core assembly and a movable armature. The movable armature is generally interlocked to trip the circuit breaker during relatively high level overcurrent conditions, such as a short circuit condition. More specifically, a generally U-shaped conductor is disposed in series with the line conductor and is disposed about a magnetic core forming a magnetic core assembly. A pivotally mounted armature is disposed at a predetermined air gap from the magnetic core assembly. When the electrical current through the U-shaped conductor becomes relatively high, such as during a short circuit condition, sufficient magnetic attraction forces are generated in the magnetic core assembly to attract the armature. Since the armature is interlocked with the operating mechanism, this action causes the circuit breaker to trip.
Various types of thermal magnetic trip units are known. In one type, the thermal magnetic unit is formed as a part of the circuit breaker. In another type, the thermal magnetic trip unit is interchangeable and is formed as a modular unit with a separate housing which can easily be inserted and removed from the circuit breaker as a unit.
Depending upon the type of electrical load to be protected, some trip units are provided with magnetic only trip units, such as in the case of electric arc welders. In other applications, a magnetic only trip unit is provided on the circuit breaker when the overload protection is provided in another device, such as a motor contactor which are generally provided with overload relays. However, for many electrical loads, such as electrical motors, both overload and short circuit protection is provided by the circuit breaker. Accordingly, both thermal and magnetic trip units, which may be adjustable, are provided on circuit breakers supplying such electrical loads. Examples of such adjustable thermal magnetic tripping units are disclosed in U.S. Pat. Nos. 4,691,182; 4,698,606 and 4,725,800, all assigned to the same assignee as the present invention and hereby incorporated by reference.
In multipole circuit breakers an overcurrent condition sensed by any pole will generally cause all the poles to be tripped. More specifically, on such multipole circuit breakers, such as three pole circuit breakers, separate thermal and magnetic trip units are provided for each pole. These thermal magnetic trip units are commonly interlocked with the operating mechanism to trip the circuit breaker for an overcurrent condition sensed by any pole. However, when the circuit breaker is connected to a dynamic load, such as an electrical motor, and one phase of the electrical load becomes open circuited, the trip unit and, specifically, the thermal unit may not respond quickly enough to prevent damage to the load. During such a condition, the electrical current in the remaining phases will gradually increase and eventually trip the circuit breaker but oftentimes not quickly enough to prevent damage to the electrical load. In addition to the expense of replacing the motor if it gets damaged, this condition can also result in incidental expenses associated with labor costs and downtime for replacement or repair of the damaged electrical load.